Especially for military applications, there is a large need to protect objects from being detected through thermal imaging and/or radar. In this respect essentially two physical and engineering problems must be solved.
On one hand the protection of the object requires screening its radiation, for instance thermal emission, and on the other hand, the hf electromagnetic radiation directed at the object should be absorbed.
Known solutions for these purposes include glass mats and shaped, bulky plastic structures with electrically conductive additives, as well as mats with felt textures to dampen and also to absorb radiation in the electromagnetic spectrum. Moreover attempts have been carried out to achieve suitable screens using two-dimensionally packed glass-, steel- and rock-wool. These screens are bulky and awkward and susceptible to environmental meteorological factors, for instance rain. Logistic difficulties follow from the bulk in transport and in handling.
It is further known to deposit and introduce suspensions or slurries of metal fibrils on and into coated and uncoated fabrics. The initial effect so achieved, that is the formation of a defined electrical surface resistance, however varies with time, i.e., during the life of this device, and accordingly renders its application unreliable and questionable.
Moreover screening means are known which essentially consist of a textile, three-ply design sewn at the edge. The two outer layers are each fitted with a colored, metallic reflective coat in order to minimize the emission and maximize the reflection.
The central ply serves as a spacer to assure the proper thickness of the enclosed insulating layer of air in the unfolded state. If in the particular application this embodiment is placed over a convex or edged, warm, emitting object, then this insulating air gap is substantially eliminated so that, in spite of the cover, there still is heat conduction from the inside to the outside. Another drawback of this design is the susceptibility of the metallic reflective layers to corrosion and the recognizable, specifically reflecting signals in the radar range. The overall system effectiveness depends on how much corrosion affects the metallic layer and to what extent this layer already has been degraded by crack formation. Cracks are formed most of all when folding and unfolding this screening means. In order to artificially imitate foliage and to create a spatial effect optically, these screens are provided with cuts. As a result, when in use, parts of the screen lift off the original plane on account of twisting and elongation. Disadvantageously, the thermal radiation passes through the gaps and the contours of the object to be masked, even if attenuated, are revealed.
An attempt has been made to circumvent this drawback by means of a two-ply netting design, with coated, areal and overlapping textiles being staggered on both nettings. This step does improve the screening efficacy, however against the tradeoff of complex handling and high professional demands on the operating personnel.